Tradeoffs in agronomic, energetic, and environmental performance of prairie and corn bioenergy cropping systems
Prairies are the native ecosystem in much of the central United States but have been largely replaced by annual crop production systems since Euro-American settlement. Cellulosic bioenergy production provides an opportunity to reincorporate prairies into agriculturally dominated landscapes, thereby enhancing the multifunctionality of these landscapes. In a 4-year, 9-ha field experiment near Boone, IA, we directly compared a corn-soybean rotation, continuous corn, continuous corn with a rye cover crop, prairie fertilized with nitrogen, and unfertilized prairie on fertile land and evaluated four performance indicators: harvestable yield, net energy balance (NEB), root production, and nutrient fluxes.
We found tradeoffs among systems in terms of the measured performance indicators. Continuous corn systems were the highest yielding averaging 13 Mg ha-1 of harvested biomass, whereas fertilized and unfertilized prairies produced the least harvested biomass at 8.8 and 6.5 Mg ha-1, respectively. Mean NEBs were highest in continuous corn systems at 45 GJ ha-1, intermediate in the corn-soybean rotation at 28.8 GJ ha-1, and lowest in fertilized and unfertilized prairies at 11.9 and 11.3 GJ ha-1. Concomitant with the high yields of the continuous corn systems were the large nutrient fluxes from these systems compared to the prairie systems. Continuous corn with rye required more than three times the nitrogen inputs than fertilized prairie. Root production, on the other hand, was on average seven times greater in the prairie systems than the annual systems. Alternative cropping systems, such as prairies used for bioenergy production, can produce substantial yield, require minimal externally-derived inputs, and can be incorporated into the landscape at strategic locations to maximize the production of other ecosystem services, whereas corn-based cropping systems have an important role to play in maintaining the high productivity of agricultural landscapes.